The present invention relates to a spectroscope, and more particularly to a spectroscope capable of obtaining dispersed light from a dispersion optical system through which irradiated light from a light source, or reflected light or transmitted light from a sample to be tested, or the like (hereinafter referred to as sample light) is guided.
Dispersed light obtained by guiding sample light through a dispersion optical system sometimes shows polarizing characteristics depending on a wavelength. The reason of this is that a diffraction grating or a prism is generally disposed in a dispersion optical system and emitting light intensity varies in accordance with different polarization planes. Therefore, when employing light of a specified wavelength as sample light, accurate and precise optical measurement sometimes cannot be made because of the polarizing characteristics of the dispersed light.
A photoelectric conversion element for selectively converting a light of a specified wavelength among the dispersed lights into an electric signal, itself often has polarizing characteristics. Accordingly, the level of observation data varies according to the polarizing direction of the dispersed light in the case the dispersed light has polarizing characteristics.
To summarize the foregoing, when the polarizing characteristics of a dispersion optical system or a photoelectric conversion element or the like depend on a wavelength, the original spectrum form will be modulated by the above polarizing characteristics with the result that an accurate spectral data cannot be obtained.
In a conventional spectroscope, an optical depolarizing element is disposed at the input end or the output end of a dispersion optical system in order to reduce the influence of the polarizing characteristics of light as much as possible. Such an optical depolarizing element may be, for example, a depolarizer or an integrating sphere into which light is projected by light projecting means such as an optical fiber. The light projected into the above integrating sphere is many times reflected at the inner surface thereof and then taken out therefrom. In both cases, the polarization can be equally distributed to every polarizing direction without being converged on a specified polarizing direction. The average light intensity can be obtained in any polarizing direction by passing light through a depolarizer or an integrating sphere even though the incident light has polarizing characteristics.
However, when employing a depolarizer, only one depolarizer is not enough to achieve perfect depolarization, so it is required to use several depolarizers one over another. This costs much since the depolarizers are made of expensive crystal.
When employing an integrating sphere, it is necessary to take out the light which has been blocked in the integrating sphere by an optical fiber. The reflection rate of the reflecting layer made of barium sulfate or the like which is applied to the inner surface of the integrating sphere, greatly depends on the wavelength. More specifically, the reflection rate of the reflecting layer becomes lower as the light incident on the reflecting layer is closer to the ultraviolet region (see FIG. 5), and therefore the loss of light amount will be increased if light closer to the ultraviolet region is incident on the integrating sphere. The fact that the integrating sphere is not in a perfect spherical shape also causes further loss of light amount. Since the light amount decreases while the loss amount increases, S/N (signal-to-noise ratio) of measuring data decreases. To replenish the loss of light amount, the amount of projected light has to be increased; that is, a light source having a large capacity will be required, which dissipates high electric power being accompanied with an increase in heat generation. Consequently, trouble will be more likely to occur.